1. Field of the Invention
The present invention relates to a gas combustion type fastener driving machine, in which a fuel gas and air are stirred by a fan within a combustion chamber, a stirred air-fuel gas mixture is burned by an ignition spark, and a striking piston is actuated by a combustion pressure to drive a fastening member.
2. Related Art
A gas combustion type fastener driving machine is an apparatus in which a fuel gas supplied from a gas supply source and air are stirred to a necessary and sufficient concentration within a combustion chamber by a fan, the stirred air-fuel gas mixture is burned by an ignition spark, a striking piston is actuated by combustion energy, and a fastening member such as a nail is driven into a wood material or the like. The fan is designed to continue to rotate for a certain period of time even after a driving of the fastening member, so as to discharge an exhaust gas from the combustion chamber and cooling the combustion chamber. For example, as is shown in FIG. 6, even after a trigger switch is on and an ignition plug sparks, a fan motor continues to be actuated for a predetermined period of time (for example, 8 seconds) after a fan switch is switched off.
A battery is used as a power source in the gas combustion type fastener driving machine. The battery is most consumed by an actuation of the fan motor in a series of actions of the gas combustion type fastener driving machine. Consequently, a number of fastening members that can be driven per a single charging of the battery (a total available driving number of fastening members) is largely affected by the actuation of the fan motor.
For example, U.S. Pat. No. 5,592,580 describes an energy output control system for a fastener driving tool in which a voltage proportional to a rotation speed of a fan is sampled, so that a supply voltage to a motor is controlled based on the sampled voltage.
When the control system U.S. Pat. No. 5,592,580 is used, a sampling circuit needs to be provided in order to check the rotation speed of the fan. Thus, there is caused a problem that production costs and a surface area of a circuit board need to be increased for the sampling circuit.